Mass spectrometry



Sept. 22, 1959 J. R. YoUNKlN MASS sPEcTRoMETRY Filed Oct. 31, 1955 3 Sheets-Sheet 1 INVENTOR J. R. YouNmN HMM q lm ATTORNEYS Sept. 22, 1959 .1. R. YOUNKIN 2,905,821

MAss SPECTROMETRY Filed oct. 31, 1955 s sheets-sheet 2 INVENTOR. J. R. YOUNKIN Hbwxww 'i' ATTORNEYS Sept. 22, 1959 Filed Oct. 31, 1955 J. R. YOUNKlN MASS SPECTROMETRY 3 Sheets-Sheet 3 H AccELl-:RATING POTENTIAL INVENTOR.

J. R. YOUNKIN YHMM QM? A 7` TORNEVS United States Patent MASS SPECTROMETRY James R. Younkin, Fayetteville, Ark., assigner to Phillips Petroleum Company, a 'corporation of Delaware Application October 31, 1955, Serial No. '543,760

15 Claims. (Cl. Z50-41.9)

This invention relates to the analysis of materials by the principles of mass spectrometry.

In recent years mass spectrometers have been developed from highly specialized academic research instruments for measuring the relative abundance of isotopes into analytical tools of extreme sensitivity and accuracy. At the present time, -applications are being found for the use of mass spectrometers in process monitoring and control. Mass spectrometry comprises, in general, ionizing a sample of material under investigation and separating vthe resulting 'ions according to their masses to determine the relative abundance of ions of selected masses. The material to be analyzed usually is provided as a gas which is bombarded by a stream of electrons to produce the desired ions. Although both positive and negative ions may be formed by such electrical bombardment, most mass speotrometers make use of only the positive ions. T hese positive ions are accelerated out of the region of the electron beam by means of negative potentals. Such potentials impart equal kinetic energies to ions having like charges such that ions of diierent masses have different velocities `after passing through the electrical field and, consequently, :have different momenta. The presently know-n mass spectrometers can be classilied in one of two general groups: the momentum selection types and the velocity or energy selection types. The momentum selection instruments sort the ions into beams of different masses by the use of magnetic and/ cr electrical deecting elds. Ions of selected masses are allowed to impinge upon a collector plate to which is connected an indicating circuit. The velocity or energy selection instruments sort the ions according to the velocities or energies impar-ted to ions of selected masses by electrical accelerating elds.

When certain gases are subjected to electron bombardment, ionized particles of several masses may be formed. For example, ethane, which has a mass of 30, ionizes to form charged particles of masses 26, 27, 28, 29 and 30. Particles of mass 28 are the most abundant. Other gases of molecular weight approximately the same as that of ethane ionize to form particles of the same mass as those formed from ethane. For example, ethylene ioniZes to form some particles of mass 26. This phenomenon obviously increases the diiculties of analyzing gaseous mixtures by mass spectrometry because individual masses are not representative of a single constituent. However, the concentrations of the constituents of a mixture can be calculated by measuring the ion concentrations at a plurality of mass numbers and solving a set of simultaneous linear equations.

In y'accordance with the present invention apparatus is provided to measure ion concentrations at -a plurality of mass numbers and to transform the measurements into a set of simultaneous linear equations. A computer is provided which solves these equations automatically to provide output signals representative of the concentrations of the constituents in ther mixture being analyzed.

ICC

2 The apparatus is controlled by mechanism which sequentially focuses the mass spectrometer to detect ions of yselected mass numbers. The measured ion concentrations at these mass numbers are applied as input signals to the computer.

Accordingly, it is an object of this invention to provide apparatus to measure the concentrations of the constituents of a mixture by the principles of mass spectrometry.

Another object is to provide a linear simultaneous equation computerwhich is actuated by the output signals of a mass spectrometer.

A further object is to provide a mass spectrometer and a linear simultaneous equation computer and timing mechanism to control the operation of the spectrometer and computer.

A further object is to provide a mass spectrometer having automatic focusing means.

Other objects, advantages and features of the invention should become apparent from the following detailed description, taken in conjunction with the accompanying drawing in which:

Figure l is a schematic circuit drawing of a preferred embodiment of lthe mass spectrometer and computer of this invention;

Figure 2 is a schematic circuit drawing of the computer of Figure l;

Figure 3 is a schematic view of the timing mechanism which controls the operation of the apparatus of Figure l; and

Figure 4 is a diagrammatic representation of an operating feature of the mass spectrometer peak selector.

Referring now to the drawing in detail and to Figure l in particular, there is shown a mass spectrometer tube comprising 'a gas impermeable envelope 10i, the interior of which Vis maintained at a reduced pressure by a vacnum pump, not shown, which communicates with the interior of envelope 10 through a conduit 1:1. A sample Vof gas to be analyzed is supplied to envelope 10 through a conduit 12. A-n electron emitting iilament 13 is disposed in zone end of envelope lll and an ion collector plate 14 is vdi-sposed in the other end of the envelope. Filament 13 is connected to the secondary Winding 15 of a transformer 1'6. A current source "18 is connected to primary Winding 1'7. The center top of winding l5 is Iconnected to a negative terminal 1'9. The gas sample supplied through conduit 12. is directed into an ion-ization chamber 22 which is dened by a pair of spaced grids 23 and 24 that are maintained at ground potential. Electrons emitted from lilarnent 13 are accelerated into chamber 22 bythe potential difference between lament 13 and grids 23 and 24. These electrons bombard the gas molecules to form positive ions.

A first collimatingv electrode 28 is positioned on the second side of ionization chamber 22 and is connected to the contacter 'of a potentiometer 20. One endv terminal of potentiometer 20 is connected to a negative potential terminal 21, and the second end terminal is connected to ground. A second collim'ating electrode 29 is spaced from 'electrode 28. Electrode 29 is connected to the contactor of a potentiometer 30. The end terminals'of potentio'meter 30 are connected to terminal 21 and ground, respectively.

The positive ions produced in chamber 22 are accelera-ted by the negative potentials `applied to electrodes 28 and 29 soas to travel through tube 10 toward collector plate 14. A rst -set of three equally spaced grids 35, 36 and 37 is positioned in tube 1'0 between grid 2.9 and collector plate 14. A second set of three equally spaced grids 38, 39 and 40 is positioned -in-spaced relationv with the first set of grids. A third set of equally spaced grids 42, 43 and 44 is positioned in spaced relationship with the second set of grids. A fourth set of equally spaced grids 45, 46 and 47 is positioned in spaced relationship with the third set of grids. A fifth set of spaced grids 49, 50 and 51 is positioned in spaced relationship with the fourth set of grids.

In the mass spectrometer tube of Figure 1,. the spacings s between grids 35 and 36, 36 and 37, 38 and 39, 39 and 40, 42 and 43, 43 and 44, 45 and 46, 46 and 47, 49 and 50, and 50 and 51 are maintained equal. The spacings r 'between the centers of grids 37 and 38. 40 yand 42, 44 and 45, and 47 and 49 can be represented by the expression:

n T25(074zl) where n is an integral number, all dimensions being in inches. In one embodiment of this invention, s was 0.118 inch and the four ns, proceeding from filament 13 to collector plate 14, were five, nine, four and seven, respectively. Y

Grid 35 is connected through a resistor 55 to switches 56, 57 and 58 which are actuated by respective relay coils 60, 61 and 62. Switches 56, 57 and 58 engage respective terminals 56a, 57a and 58a when closed. Terminals 56a, 57a and 58a are connected to the contactors of respective potentiometers 64, 65 and 66. Corresponding first end terminals of potentiometers 64, 65 and 66 are connected through a variable resistor 67 to a negative potential terminal 68. Corresponding second terminals of potentiometers 64, 65 and 66 are connected through a variable resistor 70 to ground.

Five resistors 72, 73, 74, 75 and 76 are connected in series relationship between grids 35 and 51. The junction between resistors 72 and 73 is connected to grids 37 and 38. The junction between resistors 73 and 74 is connected to grids 40 and 42. The junction between resistors 74 and 75 is connected to grids 44 and 45. The junction between resistors 75 and 76 is connected to grids 47 and 49.

An oscillator 80 is provided to generate electrical signals of a radio frequency. The first output terminal of oscillator 80 is connected to the first input terminal of a feedback detector circuit 81. The second output terminal of oscillator 80 and the second input terminal of detector circuit 81 are also connected to ground. The output terminals of detector circuit 81 are connected to grids V35 and 51, respectively. The first output terminal of oscillator 80 is also connected to the first input terminal of a stopping detector circuit 82. The first output terminal of detector circuit 82 is connected to three spaced grids 83, 84 and 85 which are positioned in tube 10 between grid 51 and collector plate 14. The second input vterminal and the second output terminal of the output circuit 82 are connected to ground. A pair of spaced grids 86 and 87 are positioned in tube 10 between grid 85 and collector plate 14. These last two grids are connected to a negative potential terminal S9.

A second oscillator 90 is provided to generate electrical signals of a frequency lower than the frequency of oscillator 80. The frequency of oscillator 90 preferably is in the audio range. The first output terminal of oscillator 90 is connected to the first input terminal of a modulator circuit 91. The first output terminal of modulator circuit 91 is connected through a switch 92 to oscillator 80 so that the output of oscillator 80 is modulated by the output of oscillator 90 when switch 92 is closed. Switch 92 is closed when a relay coil 93 is not energized. The second output terminal and the second input terminal of modulator circuit 91 are connected to ground. The

first output terminal of oscillator 90 is also connected .to a switch 94 which closes to engage a contact 94a .is connected through a resistor 98 to ground.

Collector plate 14 is connected to the first input terminal of an amplifier 100 which is tuned to pass frequencies of the frequency of oscillator 90. The first ouput terminal of amplifier 100 is connected to the first input terminal of a phase detector circuit 101. The second input terminal of phase detector 101 is connected to the first output terminal of oscillator 90. The second input and output terminals of amplifier 100 are connected to ground.

The positive ions formed in chamber 22 lare acceler'j ated toward collector plate 14 by the negative potential applied to electrodes 28 and 29. During one half cycle of the output signal from oscillator '80, the electrical field between grids 35 and 36 is of such phase that ions entering this field are accelerated.` Ions which enter this field during a particular phase of the half cycle receive maximum energy. During the following half cycle of the signal from oscillator 80, the field between grids 36 and 37 is of the same phase such that the ions are further accelerated. These ions then drift through the field-free space between grids 37 and 38. The masses of the individual ions determine their times of arrival at grid 38. The ions which arrive at grid 38 at the proper time are again accelerated by the field produced from the signal of oscillator so as to receive maximum energy. The same accelerating procedure continues as the ions pass through the next ten grids in tube 10. The first output terminal of detector circuit 82 provides a positive potential which is adjusted so that only those ions which receive a predetermined maximum energy are able to pass through positive grids 83, 84 and 85 to impinge upon collector plate 14. The ions impinging upon collector plate 14 cause current to flow in the input circuit of amplifier 100. This current, which is proportional in magnitude to the number of ions impinging upon the collector plate per unit time, is amplitude modulated by the signal from oscillator if switch 92 is closed. It is this modulated component of the current which is measured by phase detector 101. The D.C. voltage from feedback detector 81 is applied to the potential dividing network comprising resistors 72, 73, 74, 75 and 76 to decelerate the ions so that the velocity of the selected ions remains substantially constant. This prevents the desired ions from drifting out of phase with the accelerating potentials.

Grids 86 and 87 are connected to negative potential terminal 89 to suppress secondary electrons which may result from ions irnpinging upon metal parts in the tube. A grounded shield 102 is positioned adjacent collector plate 14. Circuits particularly useful in the operation of the tube thus far described are shown in the copending application of Karasek and Burk, Serial No. 480,698, filed January 10, 1955, now U.S. Patent number 2,761,974.

The first output terminal of phase detector 101 is connected to the first input terminal of a servo amplifier 103. The second output terminal of phase detector 101 is connected to a terminal 104 which is engaged by a switch 105 when a relay coil 106 is energized. Switch 105 is connected to the second input terminal of amplifier 103 and engages a terminal 107 in the absence of relay coil 106 being energized. Terminal 107 is connected to switches 108, 109 and 110 which are closed by respective relay coils 111, 112 and 113 being energized. The closed contacts of switches 108, 109 and 110 are connected to the contactors of respective potentiometers 115, 116 and 117. A voltage source 118 is connected across the end terminals of each of potentiometers 115, 116 and 117. The output terminals of servo amplifier 103 are connected to a reversible servo motor 120. The drive shaft of motor 120 is connected through magnetic clutches 121, 122 and 123 to the contactors of respective po tentiometers 115, 116 and 117. Clutches 121, 122 and 123 are actuated by respective coils 124, 125 and 126 being energized. The drive shaft of motor 120' is also connected through a magnetie clutch 128 to the arms of' variable resistors 67 and 70. Clutch 128 is actuated by a coil 12,9 being energized. Rotation of motor 120 in a first direction increases the resistance of resistor 67 and decreases the resistance of resistor 70. Rotation of motor 120 in a second direction increases the resistance of resistor 70 and decreases the resistance of'resistor 67. In this manner the total resistance between terminal 68 and ground is maintained constant.

The contactors of potentiometers 115, 116 and 117 are mechanically coupled to the contactors of respective potentiometers K1, K2 and K3. These potentiometers are connected to a computer circuit 130 which is illustrated in Figure 2. A source 131 of alternating voltage is applied across the end terminals of potentiometersv K1, K2 and K3. The first terminal of voltage source 131 is also connected to the nst end terminals of potentiometers x, y and z. The second end terminals of potentiometers x, y and z `and the second terminal of voltage source 131 are connected to ground. The contactor of potentiometer x is connected to the rst end terminals of potentiometers a1, a2, and a3. The second end terminals of these potentiometers are connected to ground. The contactor of potentiometer y is connected to the first end terminals of potentiometers b1, b2 and b3. The second end terminals of these potentiometers are connected to ground. The contactor of potentiometer z is connected to first end terminals of potentiometers c1, c2 and c3. The second end terminals of these potentiometers are connected to ground.

The contactors of potentiometers a1, b1 and c1 are connected through respective resistors 133, 134 and 135 to the first input terminal of a servo amplilier 136. The first input terminal of amplifier 136 is also connected through la resistor 137 to the contactor ofpotentiometer Kl. The second input terminal of amplifier 136 is connected to ground. The output terminals of amplifier 136 are connected to a servo motor 138 which has the drive shaft thereof connected to the contactor of potentiometer x. The drive shaft of motor 138 is also connected to the contactor of the telemetering potentiometer 140. A voltage source 141 is connected across the end terminal-s of potentiometer 140, and an output terminal 142 is connected to the contactor thereof.

The contactors of potentiometers a2, b2 and c2 are connected through respective resistors 143, 144 and 145 to the iirst input terminal of a servo amplifier 146. The first input terminal of amplier 146 is also connected through a resistor 147 to the contactor of potentiometer K2. The second input terminal of amplifier 146 is connected to ground. The output terminals of amplifier 146 are connected to a reversible servo motor 148 which h-as the drive shaft thereof connected to the contactor of potentiometer y. The drive shaft of motor 148 is also connected to the contactor of a telemetering potentiometer 150. A voltage source 151 is connected across the end terminals of potentiometer 150, and an output terminal 152 is connected to the contactor thereof.

The contactors of potentiometers a3, b3 and c3 are connected through respective resistors 153, 154, and 155 Vto the irst input terminal of a ser-vo amplifier 156. The first input terminal of amplifier 156 is also connected through a resistor 157 to the contactor of potentiometer K3. The second input terminal of amplifier 156 isvconnected to ground. The output terminals of amplifier 156 are connected to a reversible servo motor 15,8 which has the drive shaft thereof connected to the contactor of potentiometer z. The drive shaft of motor 158 is also connected to the contactor of a telemetering potentiometer 160. A voltage -source 161 is connected across the end terminals of potentiometer 160, andan outputv terminal 162 is connected to the contactor thereof.`

The various relay coils and solenoids shown in Figure 1 are energized by the timing mechanism of Figure 3. A synchronous motor 170 is energized from a source of alternating current 171. The drive shaft of motor is connected through a gear box 172 to rotate a shaft 173 at a predetermined angular velocity. Shaft 173 supports three cams 174, 175 and 176. Switch arms 177, 178, and 179 are positioned adjacent respective cams 174, 175 and 1=76 so as to be moved by rotation of these cams. Switch arms 177, 178 and 179 engage respective contact-s 177'a, 178a and 179er when in respective up positions and engage contacts 177b, 178k and 179b when in respective down positions. Switch arms 177 Iand 179 are connected to the rst terminal of current source 171. Switch arm 178 is connected to contact 177:1. Contacts 177b, 178a, 17817, and 179b are connected to respective terminals 180, 181, 182 and 183. Terminals 180', 181', 182 and 183 are connected to the grounded second terminal of current source 171.

Terminals 181 and 181' are connected to -relay coils 60 and 1'11 and to solenoid coil 124, -all shown in Figure 1. Terminals 182 and 182 are connected to relay coils 61 and 112 and to coil 125. Terminals 180 and 180 are connected to relay coils 62 and 113 and to coil 126. Terminals 1,83 and 183 are connected to relay coils 93, 95 `and 106 and to coil 129. In one particular embodiment of this invention, the cams of the timing mechanism are selected so that switch arm 177 engages terminal 177a during the first 240 of rotation of shaft 173. Switch arm 178 engages contact 178a during the rst 120 of rotation. Switch arm 179 engages contact 179:1 during the time that -shaft 173 is rotating from 60 to 120, 180 to 240 and 300 to 360.

In order to describe the operation of the apparatus of this invention, reference is made to a particular analysis of a hydrocarbon mixture comprising methane, ethane and ethylene. These three materials have respective masses of 16, 30 and 26. Analysis of this type involves solving a set of simultaneous equations of the following form:

aX|b3y+CaZ=K3 In these equations the values x, y andz represent the percentages of methane, ethane and ethylene, respectively in an unknown sample. The values K1, K2 and K3 represent the mass spectrometer output signals at re- Spective masses 16, 30 and 26. The a, b and c values represent the sensitivity of the mass spectrometer at the respectiveV mass numbers. The instrument is calibrated initially by directing a pure sample of methane into the ionization chamber of tube 10 and focusing the tube sequentially to measure the ions of respective masses 16, 30 and' 26. This is accomplished by closing respective Switches 56, 57 and 58 in Sequence and adjusting respective` potentiometers 64, 65 and 66 to focus ions of `respective masses 16, 30 and 26. Atl this time switch 92 is closed iand switch 94 is open. The amplitudes of the Output signal from phase detector 101 is measured by an indicating instrument, not shown, and these values for the three mass numbers are set on respective potentiometers a1, b1 and c1. The same procedure is repeated with ethane being; directed into the ionization chamber. The output signals observed with the mass spectrometer focused on masses 16, 30 and 26 are set on respective potentiometers a2, b2 yand c2. The procedure is again repeated with ethylene being directed into the ionization chamber to obtain settings for potentiometers a3, b3 and c3. The instrument is then adjusted to analyze a mixture containing these three gases.

Duringthe rst 60 of rotation of shaft 173 switch arm 179 engages contact 179!) so that current ows through thecoils connected between terminals 183 and 183. At the same time current flows through the coils connected between terminals 1181v and 181. With reference to Figure l, it can, beseen that switch 92 is open, switch 94 is closed, switch 56 is closed and switch 105 engages terminal 104. This results in Ithe output signal from oscillator 90 being superimposed upon grid 35 of tube 10. The ion ow through tube is thus modulated at the frequency of oscillator 90 so that the signal applied through amplier 100 to phase detector 101 is of this frequency. The output signal from the amplifier 100 is compared with the output signal from oscillator 90. Phase detector 101 can advantageously be of the form illustrated in the copending application of M. C. Burk, Serial No. 431,805, iled May 24, 1954, now U.S. Patent Number 2,778,945. This phase detector comprises a pair of triodes connected in parallel relationship and having a potentiometer between the cathodes thereof. The anodes of the two triodes are connected through a potential source to a center tap on the potentiometer. The mass spectrometer output signal is aplied to the primary winding of a transformer. The end terminals of the secondary winding are connected to the respective control grids. The output signal of the audio oscillator is applied to the center tap of the transformer secondary. Filters are incorporated in the cathode circuits of the two tubes to provide a D.C. output signal. The polarity of the output signal is determined by the relative amplitudes of the two signals being compared.

The operation of phase detector 101 can be explained in conjunction with Figure 4. Chlrve 190 represents the relationship between the D.C. output signal of the mass spectrometer tube and fthe accelerating potential applied to grids 3S, 37. 38, 40, 42, 44, 45, 47, 49 and S1. The output signal is the current flow in the input circuit of amnlier 100. For a given mass number there exists a D.C. accelerating potential which provides a maximum output signal. For example, if the accelerating potential is at the value represented by numeral 191, curve 190 has a peak at point 193. Ylf the output of oscillator 90 is superimposed on the D.C. accelerating potential, the resulting accelerating potential varies periodically from the value represented by numeral 191. This is represented in Figure 4 by curve 192 being superimposed upon the D C. accelerating potential. This results in the accelerating potential varying periodically from values represented by numerals 194 and 195. Under this condition the output signal is of the form illustrated by curve 196. This signal is essentially of a frequency twice the frequencv of oscillator 90 and as such is not passed by tuned amplifier 100. The measured output signal of the mass spectrometer is thus a minimum and does not energize motor 120.

-If the D C. accelerating potential should vary in a positive direction to a point such as 197, the output signal is of the form shown by curve 201. This results from the signal of oscillator 90, which is represented by curve 192a, being superimposed upon the D.C. accelerating potential. Curve 201 varies in amplitude from values represented by numerals 198 and 199. -If the accelerating potential should vary in a negative direction to a point such as 205, the output signal is of the form shown by curve 209. This results from the signal from oscillator 90, which is represented by curve 192b, being superirnposed upon. the D.C. accelerating potential. Curve 209 varies in amplitude from values represented at 207 and 208. it can be seen that curves 201 and 209 are of the same frequency as oscillator 90 and are 180 out of phase with one another. When a signal represented by curve 201 is applied to the input of phase detector 101, motor 120 rotates in a first direction. When a signal represented by curve 209 is applied to the input of phase detector 101, motor 120 rotates in a second direction. The drive shaft of motor 120 is connected through clutch 128 to adjust variable resistors 67 and 70. The direction and degree of adjustment is sufficient to restore the D.C. accelerating potential to the desired peak value represented by point 193 in Figure 4. This operation is referred to as peak seeking and adjusts the spectrometer tube to provide a signal representative of the selected mass number which is set on the corresponding potentiometers 64, 65 or 66. During the iirst 60 degrees of rotation of shaft 173 the accelerating potential is adjusted so that the tube monitors mass 16. i

During the following 60 of rotation of shaft 173, switch arm 179 engages contact y179s so that the coils connected between terminals 183 and 183 are deenergized. This removes the output signal from oscillator from the accelerating grids of tube 10. Clutch 179 is also deenergized at this time, as is relay 106 so that switch arm engages contact 107. Relay 111 remains energized so that potentiometer is connected in the input circuit of amplifier 103. Clutch 121 remains actuated so that motor adjusts potentiometers 115 and K1. Under this condition the output signal from mass spectrometer tube 10 is compared with the voltage drop across potentiometer 115 and motor 120 is rotated in the proper direction to eliminate a difference between the compared potentials. Potentiometer 115 establishes a reference potential for balance purposes. Rotation of motor 120 also results in the contactor of potentiometer K1 being set at a value representing the output signal of the mass spectrometer tube 10 for ions having a mass of 16.

During the next 120 of rotation of shaft 173 the previously described operation repeats except that the spectrometer tube is focused at mass 30 by having potentiometer 65 connected in circuit therewith. Potentiometer K2 is adjusted in accordance wtih the output signal representative of this mass number. During the last 120 of rotation of shaft 173 the operation repeats except that the tube is focused on mass 26 and potentiometer K3 is adjusted.

The foregoing Voperation results in the computer circuit of Figure 2 being set to solve a set of three simultaneous linear equations. The voltages appearing'across potentiometers x, y and z and multiplied by the respective settings of the a, b and c potentiometers connected in cascade therewith. These summed voltages are applied to the inputs of the servo amplifiers for each respective equation. The summed voltages are compared with the voltages across the K potentiometers and the servomotors energized until the compared potentials are equal. This results in potentiometers x, y and z being set at values representing the percentages of the three components of the mixture being analyzed. If it is desired to provide output electrical signals representing these potentiometer settings, potentiometers 140, and 160 are employed. The voltages at terminals 142, 152 and 162, with respect to ground, represent the percentages ofthe three components in the mixture being analyzed.

The reason that x, y and z are solvedV for by this apparatus is mathematically explained in the Classical iterative Method or Gauss-Siedel Method, as described briefly in the Oil and Gas Journal, vol. 43, Time-Saving Computing instruments, by Morgan and Crawford, August 26, 1944, pp. 100, 102, and 105. This technique involves making arbitrary assumptions for two of the three terms x, y, or z, (e.g., y and z) and solving the equation for K1 for the third of them (e.g., x). This value of x is then used with an assumed value of z to solve the equation for K2 for y. Then, both of the solved for values of x and y are used to solve for z in the relation for K3. Errors, if any, are evidenced by different values in the assumed and solution values of x, y and z. This being an arbitrary technique, any errors, in the initial assumptions of values are resolved by using the computed values of y and z to solve for x again, and then repeating the foregoing steps until the error, if any, is reduced to a tolerable degree. Repetition converges the equa-tions on their solution.

An electrical analogy to the foregoing mathematical operations is embodied in the operating characteristics of the circuit in Figure 2. The calibration of the circuit, as explained above with respect to methane, ethane, and

ethylene, serves to set in the proper values of. a, b, and c. The value of K1, K2 and K3 are initially assumed andiset on theY corresponding potentiometers. After the: first solution, of. course these values. are those arrived at in said. rst solutions. The foregoing mathematical steps then are electrically rcpeatedi.e., whenKl is set in by the timing device of Figure 3- servomotor 138` adjusts x. to bring the servo circuit to anull.` This step is equivalent to solving1for. x with. assumed valuesof y and'z. This valueof x. is onlyy approximate,v however, and when K2 is set. in and y is solved, the nullof. the circuit for x is upset the result is that potentiometers x and y then both simultaneously adjust and go to a null, thus .simultaneously solving for x. andy. Similarly/,when z issolved forV upon setting 123, the approximations of x andy then repeat a null operation untilx, y, andz are satisfied.

Note that the electrical method doessomething the mathematical method does not, viz., it simultaneously correctsfor the initial assumed values of y. and z, if necessary, during the second and third steps, i.e., during the solutionsinvolving K2 and K3. The result is that when a value for z has finally been determinedwby the computer, the values of x and y have also been.L determined and it isnot necessary to go through subsequent iterative steps, asin the mathematical method, to correct for errors in the initial selection of values for y and z.

It should be evident that the mass spectrometer and computer described herein is in no way limited` to the analysis of a three component mixture. If a larger number of components are present, additional potentiometer networks are provided in both the focusing portion of the mass spectrometer and in the simultaneous equation computer. The speed of rotation of shaft 173 is adjusted to provide ample time for the spectrometer to focus on the selected mass peaks. The operation can be repeated at a desired frequency.

From the foregoing description it should be apparent that there` is provided in accordance with this invention a system to focus a mass spectrometer sequentially on selected mass numbers and to energize a simultaneous equation computer in accordance wtih the output signals. While the invention has been described lin conjunction with a present preferred embodiment, it` should be apparent that it is not limited thereto.

What is claimed is:

1. Apparatus toY analyze a gaseous mixture comprising mass spectrometer'- means generating a plurality of signals seriatim eachof which-is a function of alike plurality of ions insaid mixture, means responsive to said signals to provide constant outputs of amplitudes respresentative of said signals, and computer means responsive to said outputs to provide a like plurality of output signals respectively indicative of theamount of a gas iin said mixture.

2. Apparatus to analyze a gaseous mixture comprising mass spectrometer means generating aplurality of signals seriatim each of which is a function of a like plurality of ions in said mixture, a like plurality of means each one of which is responsive to a corresponding one of said signals to provide a constant output of an amplitude representative of said corresponding one signal, and computer means responsive to said outputs to provide a like plurality of output signals respectively indicative of the amount of a gas in said mixture.

3. Apparatus to analyze a gaseous mixture comprising a mass spectrometer means generating a plurality of signals seriatim each of which signals is a function of the ions of ionizable constituent gases of said mixture that have the same mass number, a like plurality of means each of which means is responsive to one of said signals to provide a constant output of an amplitude representative of -the corresponding one of said signals, and computer means responsive to said outputs to provide a like plurality of output signals respectively indicative of the amount of each constituent gas in said mixture.

4. Apparatus to analyze a mixture of a plurality of gases--comprising` mass spectrometer means for generating a like plurality of signals seriatim each of which signals is4 afunction, of, theions of, a preselectedv mass number 0f` .eachof saidgases, means responsiveto said signals to provide, constant outputs of ampltiudes representative of said signals andcomputer means ,responsive to said outputsto provide alike plurality of, output signals respectively indicativeY of the amount of each of saidV gases.

5..Ap,par atus tov analyzev a mixture of a plurality of gases comprisirigmassv spectrometer means for generating a plurality of signals seriatim each of which signals is a function of a mass.number of each of said gases, the ions of a preselectedlike, plurality of means each ofwhich is responsive to one of said signals to provide aconstant output of an .amplitude representative of the corresponding one of said signals, yand computer means responsive to said outputs to provideY a like plurality of output signals respectively indicative of the amount of each of said gases.

6. Apparatus to analyze a mixture to determine the amountsl of the constituents thereof comprising a mass spectrometer; means to focus said mass spectrometer to detect sequentially ions of constituents of the mixture having like mass numbers; a simultaneous equation computer comprising a plurality of first potentiometers, a voltage source applied across the end terminals of said first potentiometers, a plurality of second potentiometers having the end terminals thereof connected across said Voltage source, a plurality of groups of third potentiometers connected in cascade relationship with each of said second potentiometers, means to compare the sums of voltages between the contactors and iirstend terminals of correspondingthird potentiometersin each of said groups With .thevoltage between the contactor and rst end terminal of a corresponding one of said first potentiometers, andmeans responsive to each of said means to compare to adjust the contacter of the corresponding one of said second, potentiometers;` and means responsive to the output 'signalsof said mass spectrometer to adjust the con- 'tactors of respectiveones of saidv first potentiometers.

7; The combination in accordance with claim 6 wherein said mass spectrometer comprises a gas impermeable envelope enclosing means to ionize the material to be analyzed, a collector plate spaced from said means to ionize, a plurality of groups of grids spaced in a path `between saidr means to ionize and said plate, each of said groups comprisingfthree grids in spaced relation with one another, the spacings between adjacent grids being equal, the spacings'between adjacent groups of said grids being substantially where anintegral number and s is the spacing between adjacentI grids in eachgroup, and a secondgrid positioned between said collectorplateand said groups of grids; means applying a steady potential to the end grids in each of said groups of grids; means applying a potential to said second grid of polarity opposite the polarity of the ions being detected; a source of potential which fluctuates in amplitude at a rst frequency applied to the center grid in each of said groups of grids; and means connected to said collector plate to detect ions impinging thereon.

8. The combination in accordance with claim 6 wherein said means to focus comprises means to vary the amplitude of said steady potential sequentially.

9. The combination in accordance with claim 8 wherein said means applying a steady potential comprises a plurality of potentiometers connected in parallel, a source of potential and a variable impedance element connected in series with said potentiometers, switching means connecting the contactors of said potentiometers selectively to the end grid of the one of said groups of grids adjacent said means to ionize, means to actuate said switching means periodically, and means responsive to said means connected to said collector plate to adjust said variable impedance element until a maximum number of ions impinges upon said collector plate per unit time. j

10. 'I'he combination in accordance with claimt 9 wherein said last-mentioned means and said means connected to said collector plate comprise a second source of uctuating potential of a second frequency, means applying said second source to the end grid of the one of said groups of grids adjacent said means to ionize, an amplifier tuned to pass signals of said second frequency, the input of said amplifier being connected to said collector plate, a phase detector having the inputs thereof connected to the output of said amplifier and to said second source, and means responsive to the output of said phase detector to adjust said impedance element.

11. The combination in accordance with claim 6 further comprising a plurality of fourth potentiometers, means applying voltages across the end terminals of said fourth potentiometers, and means mechanically connecting the contactors of said fourth potentiometers to the contactors of respective ones of said second potentiometers, whereby the voltages between the contactors and respective first end terminals of said fourth potentiometers represent the amounts of the constituents of the mixture to be analyzed.

12. The combination in accordance with claim 6 Wherein the means responsive to the output signals from said mass spectrometer to said computer comprises a reversible motor, means to rotate said motor representative of the output signals of said mass spectrometer and clutch means to connect the drive shaft of said motor sequentially to the contactors of said first potentiometers.

13. A mass spectrometer comprising a gas impermeable envelope enclosing means to ionize the material to be analyzed, a collector plate spaced from said means to ionize, a plurality of groups of grids spaced in a path between said means to ionize and said plate, each of said groups comprising three grids in spaced relation with'one another, the spacings between adjacent grids being equal, the spacings between adjacent groups of said grids being substantially where n is an integral number and s is the spacing between adjacent grids in each group, and a second grid positioned between said collector plate and said groups of grids; means applying a steady potential to end grids in each of said groups of grids; means applying a potential to said second grid of polarity opposite the polarity of the ions being detected; a source of potential which fluctuates in amplitude at a first frequency applied to the center grid in each of said groups of grids; means superimposing a fluctuating potential of a second frequency on said steady potential; and phase sensitive means responsive to ion impingement on said collector plate at said second frequency to adjust the amplitude of said steady potential.

14. The combination in accordance with claim 13 wherein said phase sensitive means comprises an amplifier tuned to pass signals of said second frequency, means connecting'said collector plate to the input of said amplifier, a phase detector actuated by the output of said amplifier and a fluctuating potential of said second frequency, a reversible motor, means responsive to rotation of said motor to adjust said steady potential, and means to energize said motor responsive to the output of said phase detector.

15. Apparatus to analyze a mixture to determine the amounts of the constituents thereof comprising a mass spectrometer; means to adjust said mass spectrometer periodically and in sequence to detect ions of selected masses formed by the mixture being ionized; a simultaneous equation computer comprising a plurality of networks, each of said networks including a first potentiometer, a plurality of second potentiometers having first end terminals thereof connected to the contactor of said first potentiometer, the second end terminals of said second potentiometers being connected to one end terminal of said first potentiometer, a third potentiometer, a Servo motor, means connecting the drive shaft of said servo motor to the contacter of said first potentiometer, and

means applying the potential between the contacter of said third potentiometer and one end terminal thereof to the input of said servo motor; a voltage source; means `applying said voltage source across the end terminals of said first and third potentiometers in each of said networks; and means summing the potentials between said one end terminal of said first potentiometers and the contactors of corresponding ones of said second potentiometers in each of said networks and applying said summed potentials to the inputs of respective ones of said servo motors; and means responsive to the output signals of said mass spectrometer representative of said selected masses to adjust the contactors of respective ones of said third potentiometers.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES A Computer for Solving Linear Simultaneous Equations, Berry et al., Journal of Applied Physics, vol. 17, No. 4, April 1946, pp. 262,-272.

UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION 27e-bent No., 2,905,821 September 22, 1959 James EL. Younkin It is herebjr certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Gomi 1G, linel 12 strike-- out "e" and insert tbe same bef-ore "likeu in line'l 13; lines l2 'and 13 .Strike out "the ions of ,a preselected" `and insert the Semev after "function of" in line' l2, seme column; line4 63, for .L v

one claim referencenumeral "6 reed am 7 en.,

Signed and, sealed this 7th day of June 1%@ Tf) ttest:

EARL ROBERT C. WATSON Attesting Officer Commissioner of Patents 

